In the information-oriented society of today, various transmitting means are used to transmit electrical and electronic information such as sound, picture, text data, binary data, etc. Of such electrical and electronic information, low quality sound, monochrome still picture at low speed, character data at low speed, and binary data at low speed are transmitted by public telephone line as electric signals, and monochrome still picture at high speed, character data at high speed and binary data at high speed are transmitted by ISDN (Integrated Services Digital Network) line as an electric signal. High quality sound and moving picture are transmitted by terrestrial wave broadcasting, satellite broadcasting or CATV as a modulated radio wave or by optical fiber as modulated light.
In the present information-centered era, attention is now focused on interactive information systems as a promising major information system in future. The interactive information system is a system, in which information is selectively received and positively utilized by the general public, who, hitherto, have been merely receivers of the one-way information sent to them.
Interactive information systems currently used are answering systems using an automatic voice response system via public telephone line, videotex systems represented by CAPTAIN (Character And Pattern Telephone Access Information Network) using still picture, and VRS (Video Response System) using moving picture via dedicated line.
Of these interactive information systems, the answering system is disadvantageous in that sufficient information cannot be obtained because it depends upon audio information only and that input and output data cannot be visually confirmed.
The videotex system has drawbacks in that there is a limitation in the contents to be displayed because texts and pictures are displayed by using character codes, and the picture information using character codes provides a smaller amount of information than a natural picture.
The VRS system has no limitation in the contents of display because a natural moving picture can be used, while communication cost is expensive because a wide band dedicated line must be used.
On the other hand, various information services such as television shopping, application or subscription, weather forecast, traffic information, etc. are offered in the currently used television system, although these are not interactive. Most of the picture information needed in these information services is still picture information, and moving picture information is needed in very rare cases. Thus, in the current television system offering these information services, a still picture is broadcast as moving picture. Specifically, by transmitting several hundreds to several thousands of the same picture, a still picture is displayed on a television set.
Therefore, the transmitting cost of the still pictures is very expensive, and an interactive information service for transmitting still pictures to match the demand of the users is not currently available.
For example, television shopping is one of the information services using pictures. However, in the television shopping practiced to date, only the one-way product information, transmitted by the broadcasting station, is utilized, and interactive information service in which the desired picture from product information is displayed on the television set according to the intention of the users and the users carry out shopping based on the contents of the display is not practically available.
A television picture is composed of frame units. In the NTSC system adopted in Japan, the picture is sent at a rate of 30 frames per second. If one still picture is transmitted for each frame, 30 natural still pictures are transmitted within a second.
As a still picture broadcasting system based on this principle, there is a system called the "time-division still picture broadcast system".
FIG. 1 represents a drawing to explain the time-division still picture communication system.
In the time-division still picture broadcast system shown in FIG. 1, still pictures 3-1, 3-2, 3-3, 3-4 . . . are photographed at first by independent television cameras 4-1, 4-2, 4-3, 4-4 . . . at a still picture broadcasting station 1. Next, these still pictures are composed to television signals comprising frames 5-1, 5-2, 5-3, 5-4 . . . , and these are transmitted to still picture receiving devices 2-1, 2-2, 2-3, 2-4 . . .
Upon receipt of the television signals, necessary frames are stored at frame memories 6-1, 6-2, 6-3, 6-4, . . . at the still picture receiving devices. Next, the stored frames are repeatedly read out from the frame memories and are displayed on display units 7-1, 7-2, 7-3, 7-4 . . . as still pictures.
Selection of the necessary frames and recording them to the frame memories are carried out by the procedure such as inserting a frame identification signal to the horizontal scanning line during the vertical retrace interval of each frame.
In one frame, two field pictures comprising different picture components are superimposed by interlace scanning.
Each of the frame pictures is a complete natural picture, while a field picture is not a complete natural picture because its amount of information is only one-half of that of the natural picture. However, when compared with the picture based on character codes, it may be referred as a natural picture, which provides satisfaction. In a broadcast of still pictures, twice as many field pictures are transmitted.
An interactive still picture information service system has been proposed, in which a still picture information service is requested by, for example, a public line and the still picture information service is offered by the "time-division still picture broadcast system" in response to such request. FIG. 2 shows a general outline of the system.
This system comprises a still picture broadcasting station apparatus 8 for broadcasting a still picture by the time-division still picture broadcast system, an information provider apparatus 9, a user apparatus 10, and a data communication device such as a telephone set 15. A terrestrial broadcasting wave 12 or satellite broadcasting wave or CATV radio wave is used to connect between the still picture broadcasting station apparatus 8 and the user apparatus 10, and a communication line 11 such as public line or CATV line is used to connect the telephone set 15 with the information provider apparatus 9. A communication line such as public line or dedicated line is used to connect the information provider apparatus 9 with the still picture broadcasting station apparatus 8.
The information provider apparatus 9 may not be used. In this case, the still picture broadcasting station apparatus 8 is directly connected with the user apparatus 10 via a communication line such as a public line or a dedicated line.
The user apparatus 10 comprises a set-top box 14 for receiving the still picture, a display unit 13 and a data communication device such as a telephone set 15. The set-top box 14 is connected to a television antenna for receiving the still picture broadcast, a television antenna for receiving a satellite broadcast, or a coaxial cable for CATV. The set-top box 14 is connected to the display unit 13 such as a television set. The telephone set 15 is connected to a communication line 11 such as a public line or CATV line.
In this system, when a user wishing to receive the information service, calls the information provider apparatus 9 using the telephone set 15 via the communication line 11 and requests transmission of the desired still picture, the request is transferred to the still picture broadcasting station apparatus 8. As a result, the desired still picture 16 is broadcast, and the desired still picture 17 is displayed on the display unit 13 by the user.
In the interactive still picture information service system as described above, selection of necessary frames and recording of them in frame memories are performed in such a manner that a frame identification signal is inserted into the horizontal scanning line in a vertical retrace interval of each frame by the still picture broadcasting station apparatus 8, and this frame identification signal is detected by the user apparatus 10.
For this purpose, it is necessary to provide means for inserting the frame identification signal to the horizontal scanning line in the vertical retrace interval of each frame at the still picture broadcasting station apparatus 8 and also to provide the user apparatus 10 with means for detecting the frame identification signal. This naturally means that the still picture broadcasting station apparatus 8 and the user apparatus 10 will be more complicated.